Despite being very happily married to my soul mate, with whom I have two much-longed-for children, I have recently experienced periodic bouts of wanting to burn my life down to the ground and start again. "I'm 39, and my life is half over," I would think to myself late at night. Shouldn't I be seeking adventure? Maybe we should sell everything and all move to Newfoundland!

Or maybe we should have a third child? A recent accidental pregnancy and subsequent miscarriage (my first) shocked me into facing the reality that my fertility window is rapidly closing. Should I be making a last-gasp lunge for that goal instead, and embrace the magical chaos that comes with children? Or should I plunge headfirst into writing that book I've been thinking about for two years?

Then came the wacky behaviour: a sudden, short-lived crush on a bass player in a Canadian rock band, promoted by mournful feelings that I will never be in a rock band (a goal I've never had before). I even call the bass player to ask whether all the songs he writes about being middle-aged indicate that maybe he's having a crisis, too. (I hope he will say that a rocker's life provides no inoculation against the fear that you should be doing something else with your life, and that this will comfort me in some way. No such luck.)

Like a New York City ghetto at 3am, the female midlife crisis is a place where few feel comfortable to tread. This was never more evident than when I found myself knee-deep in one, completely blindsided by a sudden rash of uncomfortable feelings.

Psychologist Robyn Vickers-Willis says it's very common for women aged between 35 and their late 40s to feel unmoored by feelings of depression, emptiness, bewilderment and a sudden desire for change, with no idea where any of it is coming from. During "midlife transition", our psyche, she says, "encourages us to move from having a sense of identity based on how we're conditioned to see ourselves" - that is, based on how others expect us to be - "and more to how we truly are, and then to create a life based on that".

Why, God why, are women so ignorant about this process? I approached countless women for this article, and almost every one of them said, "Midlife crisis? Women have midlife crises?"

For one thing, most of the research on midlife has been conducted on white men. And, as American writer Sue Shellenbarger puts it in her book The Breaking Point: How Today's Women Are Navigating Midlife Crisis, the triggers of male and female midlife crises are markedly different. A woman is more likely to feel unstable in midlife as a result of family problems, feelings that she hasn't met her standards or goals as a parent, or because earlier goals have been shoved aside. In contrast, men are more likely to feel shaken by "work or career issues". While women tend to look inwards, to find out what is missing from their lives, men generally look outwards.

I could add that our experience is also largely absent from popular culture. The male midlife crisis has been at the centre of countless films and TV shows like American Beauty, City Slickers and Louie. But women? There's virtually nothing. (Judd Apatow's new film, This Is 40, which opened in Australia this month and looks at a couple struggling with midlife blahs, is a rare exception, in that it is not solely focused on the male experience.)

It's no surprise, then, that when first confronted with the question about whether a midlife crisis prompted her to start a travel company at the age of 40, radio presenter Sami Lukis dismisses my theory as "pretty funny". It's only later, in between sips of coffee at a Kings Cross cafe, that a confession that verges on stream-of-consciousness comes out.

It all started, says the co-host of Sydney Mix 106.5's Ant & Sami Lukis Show, two and a half years ago, when she had just experienced the worst year of her life. She was stuck in "the least rewarding job of my career", a long-term relationship had just ended, her grandmother had died, and she'd discovered her fertility was in "rapid decline".

"I found myself in that moment of my grandmother dying, and all of her family around her at her bedside," says Lukis. "She was there on her deathbed with her children and her grandchildren and some of her great-grandchildren, and I thought, 'Wow, I don't have any of this', you know? 'I'm single, I don't have kids. This is what life's about.'"

It was then that Lukis tried unsuccessfully to have a baby - first by researching IVF and sperm donation, later by trying to conceive naturally with a new-ish boyfriend. She subsequently decided to take a year off and launch her company, which offers tours of New York City for women aged 30 and up. So, yes, on reflection, she had a life-changing crisis, and it was at midlife. She believes that, for many women, a midlife crisis can be "an empowering experience, a positive thing".

"When you think of the male midlife crisis, it's all a bit of a joke," she says. "All the clichés - the ponytail and the Porsche and the having an affair with the secretary - they're all kind of negative things. Whereas for a woman, it's finding a sense of self. And I know that's where my tours have tapped in."

She describes the experience of one of the women she took on tour, who was married with three children: "She said, 'Sami, this has been a life-changing experience for me. This is the first time in literally 15 years that I've put myself first, and had time for me.' And she was crying."

Vickers-Willis, author of the book Navigating Midlife: Women Becoming Themselves, says there have long been societal pressures that discourage women from tossing off others' expectations of who they should be and embracing who they are at their core - and how they truly want to live their lives. This growth, she says, can threaten the still-traditional "status quo" of wife as nurturer and husband as provider.

A long-term study of the evolving physical and mental health of 40,000 Australian women backs this up. The Australian Longitudinal Study on Women's Health, which released its most recent results last September, revealed that many middle-aged women found themselves too busy taking care of other people to explore their own needs and desires.

"They are just, quite frankly, too busy," says Meredith Taverner, a researcher from the University of Newcastle's Research Centre for Gender, Health and Ageing who worked on the study. "They don't afford themselves the luxury of a midlife crisis. They've got too much responsibility."

The price that women can pay if they don't discover who they truly want to be, though, can be high. Sue Shellenbarger, who is also a columnist with The Wall Street Journal, says that 20 years of denying her lifelong "hell-bent" desire for adventures in the wild and a more "rustic" life eventually led her, at 49, to a "meltdown", thoughts of suicide, and a dislocated collarbone in a quad bike accident.

She had convinced herself that her identity lay in professional "achievement", forging a career in newspapers, raising three stepchildren and two birth children in the suburbs. She writes that she "fell into the trap of doing too much".

"I hewed for a long time to too confining a self-image," she writes in The Breaking Point. "My pose as the perfect wife, worker and mother was exactly that: a pose, too constraining to be sustained."

And when a marriage breakdown, her father's death and thoughts of a looming empty nest bore down upon her, she found that the desires she'd ignored for so long began to overwhelm her. Instead of incorporating small trips to the outdoors in manageable ways, she entered a reckless period of playing hooky from her job, escaping to the forest, desert or mountains on dangerous adventure trips, and, at times, neglecting her family. "It really took me a while to really understand what was happening," says Shellenbarger.

Robyn Vickers-Willis has seen women turn to other damaging behaviour after they've ignored signs that they need to be re-evaluating their life. Some become addicted to shopping, nearly bankrupting themselves. Others initiate an unhealthy obsession with extreme exercise.

A friend of mine in Sydney tells me of two friends, both 45-year-old women with two children, who are trying to fill a midlife feeling of emptiness (in one case triggered by a divorce, in the other by an unsatisfying marriage) with reckless affairs. Her married friend, she says, is having "dangerously risky affairs, doing it anywhere - in cars, on desks. It's like she almost wants to get caught."

But, says Shellenbarger, the midlife crisis is not something to be feared but, rather, embraced. After putting an end to her out-of-control adventures, she began incorporating the wild into her life in manageable ways. She started doing farm work on a friend's homestead, and now, at 61, she has found love again with an outdoorsman with whom she goes on numerous hiking and adventure trips.

And the majority of the 50 women Shellenbarger interviewed for her book used their midlife crises as a jumping-off point for rewarding creative and constructive pursuits, like launching new businesses or becoming artists. "We gain a new understanding of our limits," Shellenbarger says of women who come out the other side after a midlife crisis. "And we develop a new sense of meaning and direction to guide us through the rest of our lives."

As for me, I've decided that if I've only got a few decades of life left, I will regret seeing them out without experiencing, one last time, the mad, joyous (and sometimes terrifying) fun house that comes with welcoming another child into your family.

So I'm pregnant - and deliriously happy about it. There'll be time to write a book after that.

THE SIGNS

1. Constantly asking yourself: "Am I the person I really want to be?"

2. An overwhelming desire to tackle a desire or goal long forgotten since childhood.

3. Suddenly wanting another child.

4. A new addiction to anything, from sex to shopping to extreme sport.

5. Unexplained depression, listlessness or lethargy.

6. The feeling that you're trapped in a life you don't want.

7. Constantly asking yourself: "Is this all there is?"

8. Feeling confronted by mortality, and the wish to live a life of greater meaning.

9. Out-of-control emotions.

10. Unexplained crushes on a bass player from Canada.

- Daily Life

Have you experienced a mid-life crisis? How did you cope and how did it change you?